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  • Articles: DFG German National Licenses  (103)
  • 1990-1994  (63)
  • 1985-1989  (40)
  • 1
    Electronic Resource
    Electronic Resource
    Relativistic and nonrelativistic plasma dispersion functions (1989)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 30 (1989), S. 2484-2487 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A number of new results involving the functions that determine the emission, dispersion, and absorption of waves in nonrelativistic and weakly relativistic plasmas are presented. These results comprise series, integrals, recursion relations, symmetry properties, interrelations, approximations, and connections with standard transcendental functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.528528
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  • 2
    Electronic Resource
    Electronic Resource
    A prospective trial of computed tomography in the staging of ovarian malignancy (1985)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 92 (1985), S. 0 
    Details
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Summary. Thirty patients, thought clinically to have ovarian tumours, were studied prospectively by pre-operative computed tomographic (CT) scans of the abdomen and pelvis. In six patients (20%) small metastases in mesentery, omentum and on subdiaphragmatic peritoneum were not detected by the scans. CT did not improve the accuracy of staging or assist the surgeons by drawing their attention to disease which they might otherwise have missed. Although CT gives an elegant demonstration of anatomy, it is not an alternative to extended laparotomy in patients with ovarian tumours.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-0528.1985.tb01116.x
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of annealing on TlBaCaCuO thin films (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 660-662 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the effects of high-temperature anneals on sequentially deposited TlBaCaCu films in an environment containing O2 and TlOx . From Auger electron spectroscopy depth profiles, it was found that Tl was quite volatile and can be easily eliminated from the thin films after a short treatment at 830 °C. However, the Tl can be incorporated in the films after appropriate treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100911
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Gastric Function in Eating Disorders (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 575 (1989), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1989.tb53266.x
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  • 5
    Electronic Resource
    Electronic Resource
    Density fluctuations in strong Langmuir turbulence: Scalings, spectra, and statistics (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 3017-3023 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A recently developed two-component model of strong Langmuir turbulence is applied to determine the scalings, spectra, and statistics of the associated density fluctuations. The predictions are found to be in excellent agreement with extensive results from numerical solution of the Zakharov equations in two and three dimensions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859368
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  • 6
    Electronic Resource
    Electronic Resource
    Driven random-phase three-wave interactions: Cycles, bursts, and stochasticity (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 3524-3532 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Steadily driven, undriven, and stochastically driven three-wave decay processes involving groups of random-phase waves are investigated analytically and numerically. Steadily driven systems in which one product wave is suppressed exhibit neutrally stable Lotka–Volterra cycles, as for the true two-component case, whereas three-component systems are stable below a critical driver strength and unstable beyond that point. Initially unstable, but undriven, systems produce bursts of product waves, after which the parent waves fall to a final level that is an exponentially decreasing function of their initial level. Three-component systems where the product waves have near-equal dissipation rates are an exception to the latter behavior; in such systems the final parent-wave level is almost independent of the initial one. Stochastic driving gives rise to bursts of product waves in a cycle of fluctuating period, whereas a low-level noise source tends to stabilize the system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860360
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Transit-time damping and the arrest of wave collapse (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 545-554 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Power dissipation by transit-time damping is investigated analytically and numerically using a perturbation expansion and a test-particle code, respectively. Excellent agreement between the two methods is found for both one-dimensional and multidimensional systems. It is shown that the local power dissipation can take on positive or negative values depending on position, implying that particles not only carry off energy from localized fields, but redistribute it within them. The results are applied to estimate the arrest scales of the collapsing wave packets found in strongly turbulent plasmas. Arrest scales in the ranges (14–23)λD and (16–26)λD are found for two- and three-dimensional wave collapse, respectively. These estimates are consistent with results from particle-in-cell simulations, which yielded arrest scales of ∼14λD in 2D and ∼20λD in 3D, and with experimental results that implied arrest at scales of (17–30)λD in 3D. The previously problematical outcome that 3-D collapse is arrested at a longer scale than in 2D, despite its stronger nature, results because the larger fraction of high-velocity particles in the 3-D plasma velocity distribution leads to stronger transit-time damping than in the corresponding 2-D system. It is argued that transit-time dissipation will arrest the collapse of particularly intense wave packets at even longer scales due to the increase in the local Debye length caused by localized heating near the center of these wave packets and due to the formation of high-velocity tails by transit-time acceleration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859905
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Two-component model of strong Langmuir turbulence: Scalings, spectra, and statistics of Langmuir waves (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 2999-3016 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-component model of strong Langmuir turbulence is developed, in which intense coherent Langmuir wave packets nucleate from and collapse amid a sea of low-level background waves. Power balance between these two components determines the overall scalings of energy density and power dissipation in the turbulence, and of the rate of formation, number density, volume fraction, and characteristic nucleation time of collapsing wave packets. Recent insights into the structure and evolution of collapsing wave packets are employed to estimate the spectra and field statistics of the turbulence. Extensive calculations using the Zakharov equations in two and three dimensions demonstrate that the predictions of the model are in excellent agreement with numerical results for scalings, spectra, and the distribution of fields in the turbulence in isotropic systems; strong support is thus found for the nucleation model. The scaling behavior proves to be insensitive to the form of the damping of the waves at large wave numbers. Wave collapse is approximately inertial between the nucleation and dissipation scales, yielding power-law energy spectra and field distributions in this range. The existence of a fixed arrest scale manifests itself in exponentially decreasing energy and dissipation spectra at high wave numbers and exponentially decreasing field distributions at high field strengths. It is suggested that such an exponential decrease may explain the field distributions seen in recent beam–plasma experiments. Generalizations to turbulence driven anisotropically by beams or governed by equations other than the Zakharov equations are outlined. It is shown that a previously unrecognized scaling observed in beam-driven systems is correctly predicted by the generalized model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859367
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Conditions for the validity of unmagnetized-plasma theory in describing weakly magnetized plasmas (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 525-534 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An investigation is made of the conditions under which the expression for the dielectric tensor from magnetized-plasma theory may be approximated by that from unmagnetized-plasma theory. Surprisingly, the conditions usually quoted are shown to be inaccurate chiefly because they make no reference to the form of the plasma distribution function. Corrected conditions depend strongly on the distribution function and their application is thus highly problem-dependent. For completely arbitrary distributions these conditions are generally stronger than the commonly quoted ones for weakly damped waves. By contrast, the conditions applicable to axisymmetric distributions can be weaker than some of those commonly quoted. A geometric interpretation of the revised conditions for axisymmetric distributions is given in terms of the resonance ellipses of cyclotron maser theory and is illustrated with reference to dispersion and instability of Langmuir and Bernstein waves in weakly magnetized plasmas. These results apply to all weakly magnetized plasmas that can be described by the linearized Vlasov equations and imply that some investigations which have used the commonly quoted conditions to justify use of unmagnetized-plasma theory may be in error on this point.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866834
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Weakly relativistic dispersion of Bernstein waves (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 107-114 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Weakly relativistic effects on the dispersion of Bernstein waves are investigated for waves propagating nearly perpendicular to a uniform magnetic field in a Maxwellian plasma. Attention is focused on those large-wave-vector branches that are either weakly damped or join continuously onto weakly damped branches since these are the modes of most interest in applications. The transition between dispersion at perpendicular and oblique propagation is examined and major weakly relativistic effects on dispersion at perpendicular propagation are found to persist at other angles; these effects can dominate even in low-temperature plasmas. A number of simple analytic criteria are obtained which delimit the ranges of harmonic number and propagation angle within which various types of weakly damped Bernstein modes can exist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866557
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